The present invention relates to a fluid heater system, and particularly to a single tank fluid heater system with an exterior temperature sensor.
Instantaneous water heating systems have long been used in applications including, for example, dishwashing in commercial food establishments. There is a tight control window in which the water outlet temperature must be maintained in order to provide safe and consistent operation within a predetermined operating temperature range for a specific application. Maintaining the water outlet temperature within this tight control has been an ongoing problem for this type of heater.
U.S. Pat. No. 4,638,944 (the '944 patent), which is incorporated herein by reference, is directed to one solution to the temperature control problem. Specifically, the '944 patent addressed the problem of temperature control in a compact, high volume point of use instantaneous water heating system by using two individual water heaters, each with an "instantaneous" burner, heat exchanger, and an exterior temperature sensor. The burners of the instantaneous heaters would alternate between high and low heat asynchronously. The '944 system provides a consistently controlled outlet temperature by averaging four variables: the temperature within the lower portion of the accumulator tank measured by a thermostat therein; the temperature at the outlet of the first heat exchanger; the temperature at the outlet of the second heat exchanger; and the water flow through the entire unit.
The use of the dual heaters operating asynchronously as described in the '944 patent helped to permit the use of a smaller-sized accumulator tank adjacent the use point, since no large accumulator volume is required to smooth out water temperature fluctuations. However, to properly control temperatures, dual heaters were absolutely necessary because the burners known at that time were not capable of actual instantaneous heating requiring a short heat up time period. Further, the temperature sensors that existed at the time at which the '944 patent was applied for were neither quick nor accurate over time, resulting in poor reliability.
Although the '944 system contemplates a single auxiliary heater, the advantages associated with temperature control would be decreased, because the dual heaters are needed for averaging and accuracy.
What is needed, therefore, is a point of use instantaneous water heating system that is able to provide hot water on demand at a temperature within a predetermined tight control window.